In a semiconductor production process, a hole (e.g., contact hole) is formed by plasma-etching a specific area of a silicon oxide layer formed on a substrate. When forming such a hole, the open area of the hole tends to have a blocked shape (i.e., necking tends to occur). In recent years, contact holes tend to be reduced in diameter and increased in aspect ratio due to miniaturization of semiconductor devices. Therefore, development of technology for forming a contact hole having a very small diameter and a high aspect ratio in a substantially vertical shape without necking has been desired.
Patent Document 1 discloses a method of forming a contact hole having a very small diameter and a high aspect ratio in a substantially vertical shape by selectively utilizing two or more etching gases (process gases) containing a fluorocarbon.
However, since the method disclosed in Patent Document 1 requires use of two or more process gases, a complicated gas switching operation is necessary. Therefore, the method disclosed in Patent Document 1 is not satisfactory from the viewpoint of industrial production efficiency.    Patent Document 1: JP-A-2006-278436